The present invention relates to moving picture coding for appropriately changing a coding scheme between intra-frame predictive coding (intra coding) utilizing spatial redundancy and inter-frame predictive coding (inter coding) utilizing time redundancy, and more particularly relates to a technique for achieving improvement of coding efficiency and fast coding processing (motion detection) in coding of an image with a fast motion.
FIG. 8 is a block diagram illustrating an exemplary configuration of a known image coding apparatus (encoder). FIG. 9 is an illustration conceptually describing inter-frame predictive coding (inter coding). In FIG. 8, an image signal received from an image input section 51 is temporarily stored in a frame memory 52. In the case of intra coding, DCT (in a DCT section 53), quantization (in a quantizing section 54) and Huffman coding (in a Huffman coding section 55) are performed to 1-frame image data, that is, coding utilizing spatial redundancy in the same frame is performed. At this time, inverse quantization (in an inverse quantization section 56) and inverse DCT (in an inverse DCT section 57) are performed to quantized stream data, and then obtained data is stored, as a predictive reference image frame, in a frame memory 58.
On the other hand, in the case of inter coding, the reference image frame (FIG. 9A) stored in the frame memory 58 and a current image frame (FIG. 9B) stored in the frame memory 52 are compared with each other in a motion detection section 59 and then a motion vector is obtained for each macroblock or for each frame (FIG. 9C). Then, motion compensation is performed to the reference image frame in a motion compensation section 60 using the motion vector so as to generate a reference frame (FIG. 9D) and a difference between the reference frame and the current image frame (FIG. 9E) is subjected to DCT, quantization and Huffman coding and then obtained data is transmitted. The detected motion vector is also subjected to Huffman coding and then transmitted. At this time, the inverse quantization and inverse DCT are performed to quantized difference data, and obtained data is added to motion compensation predictive data output from the motion compensation section 60 and then is stored in the frame memory 58. The obtained data is a predictive reference image frame for a subsequent frame (FIG. 9F).
As for known techniques, Reference 1 (U.S. Pat. No. 5,477,272) discloses a technique in which in motion detection, wavelet transform is performed to generate a size-reduced image and then a correction is made based on a motion vector obtained using the size-reduced image to obtain a final motion vector. Also, Reference 2 (U.S. Pat. No. 6,219,383) discloses a technique in which in motion detection, wavelet transform is performed to generate a size-reduced image, as in Reference 1, a motion vector obtained using the size-reduced image is compared with the motion vector of a macroblock located in the periphery of a target macroblock for search, and then a correction is made.